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The Drill Rod 

Make] Projects 

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build, hack, tweak, share, discover,- 

The Drill Rod 

Written By: Russ Byrer 



Drill (1) 

Use the one that will power the bike 


Drill bits (1) 
for metal 


Hammer (1) 

Hex/ Allen wrenchs (1) 
common sizes 

Marker (1) 

Milling machine (1) 

/ used my Smithy ( 

combination milling machine and lathe. 

Pliers (1) 

Ruler (1) 

Screwdrivers (1) 
common sizes 

Tap and die set (1) 

Mini bike (1) 

This has been discontinued by Razor: 

check flea markets and eBay 


Gear box (1) 

part #RAB- 1 from Torque Transmission 

( $89 

Drill (1) 

Make sure the chuck opens enough to 
accept the shaft of the gearbox. I used a 
Bosch 36- volt Litheon. 

Rear wheel assembly (1) 

part #W1 51 25090048 from Razorama 

(, $26 

Sprocket (1) 

part #2737T121 from McMaster-Carr 

( $6 

Roller chain (1) 
McMaster-Carr #6261 K283. $10 

Connecting link (1) 
McMaster-Carr #6261 K1 08 

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The Drill Rod 


/ bought mine on eBay for $20. 

Throttle cable (1) 

Bar stock (1) 


U-channel (1) 

Scraps (1) 

for the kicks tand extension and hinged 
platform. I used some old oak and a 
broken teak paper towel holder I found in 
the trash can at the marina. 

Knobs (1) 

Ball plunger pin (1) 

Zip ties (1) 

for kickstand extension 

Bicycle seat (1) 

Screws (1) 

Washers (1) 



I have a 25' cruising tugboat in Florida, and I wanted a small, lightweight ride that I could 
keep onboard for making beer and ice runs when I pull into a marina. After seeing a short 
segment on TV about a cordless-drill-powered bike at a hardware convention, I decided to 
build my own. 

Behold the result: the Drill Rod. Equipped with a 36-volt drill, this brute accelerates from to 
10mph in just 2 seconds and is responsive enough to do tricks like standing on its back 

As for styling, it's been said that when I'm on my Drill Rod, I look like a circus bear on a 
tricycle (duly note the photo in Step 1). You will not attract potential romantic partners when 

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The Drill Rod 

riding this. Trust me. 

When I started the project, I contacted the company that made the bike I saw on TV and 
asked if they could just sell me the right-angle gearbox that enables the center-mounted drill 
to drive the rear wheel. But they refused; they would only sell a finished bike. 

I continued looking for ways to build my own. At a flea market, I found a tiny battery-powered 
bike for kids called the Electric Punk, made by Razor. I bought it for $60 and took it home. 
With its small battery and motor, I knew it was underpowered for what I needed, and its 7" 
rear wheel looked too small to support the weight of an adult. 

On flat pavement, the Electric-Punk only went 5mph, and it couldn't even pull me up my 
driveway slope. But its small frame was perfect for the project. 

For the engine, I used a 36V Bosch Litheon drill, which was the most powerful cordless I 
could find. I bought it reconditioned through Amazon for $219. I also found a nice, small 
right-angle gearbox (1:1 ratio) made by Torque Transmission, model #RAB-1, which was 
rated at 1/3HP at the drill's maximum speed of 1,800rpm. 

Step 1 — Beef up the rear wheel. 

• I took the Electric Punk apart and went to work. I stripped the plastic shells, the battery, 
the motor, and the motor thumb trigger on the right handlebar. I threw the useless little 
motor in the trash. 

• First I replaced the 7" rear wheel with a larger rear wheel and sprocket assembly for the 
Razor Mini Chopper, which takes a 9" tire. This would carry weight more comfortably. I 
don't know if this was strictly necessary, but I knew I wanted it to make the bike look 

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The Drill Rod 

Step 2 

• To fit the 9" wheel onto the bike, I 
needed to relocate the axle farther 
back on the swing arm, so I drilled 
new axle holes about 3 A" behind the 
original ones, and then moved the 
brake pads back to match. 

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The Drill Rod 

Step 3 — Mount the right-angle gearbox. 

• Next came the gearbox. I screwed an 18-tooth sprocket to the right side of the gearbox, 
and then mounted the box where the bike's original motor attached. 

• The original mount was a plate that slid up and down for adjusting the chain's tension, 
which meant that I couldn't just drill holes through and bolt the gearbox on with nuts on the 
other side. So I made my own mounting plate that screwed into the original motor's holes, 
with blind-tapped holes for the gearbox mounting screws to sink into. 

• I used Google SketchUp ( ) to design the mounting plate, as well 
as the throttle mechanism and seat post hinge mechanisms that I added later. Download 
the designs here . 

• I used a straightedge to make sure the gearbox sprocket lined up accurately with the 
wheel sprocket. This is important because if the sprockets don't line up, the chain may slip 
off. Then I cut the chain to length and connected the 2 ends with a connecting link. 

• The larger wheel makes the bike's kickstand too short, so I made an extension out of 
scrap oak. To secure it, I chiseled out a groove that fit the curved lower part of the original 
kickstand, then drilled the wood and strapped it on with heavy-duty nylon zip ties. 

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The Drill Rod 

Step 4 — Mount the throttle. 

• I attached the drill to the gearbox shaft directly, just the way you would put a drill bit in it. 
The problem was, the drill had so much torque that the chuck just slipped around the shaft 
and quickly chewed it up. I found this out the hard way, so I had to make a replacement 

• The original gearbox shaft was " in diameter, but I made the new one V2" thick and then 
machined 3 equally spaced flats around its sides, giving it a rounded triangle shape. The 
resulting shaft was beefier and easier for the drill chuck to clamp down on. 

• The Razor came with a thumb-operated switch that simply turned the motor full on or off. I 
replaced this with a motorcycle-style handlebar twist grip that pulls a throttle cable. 

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The Drill Rod 

Step 5 

• This was easy; you just take off the old hand grip, slip the new one over the handlebar, and 
tighten the screws. The throttle cable's other end attaches to a small lever that pulls the 
drill's trigger, just like you would with your finger. This speed control method is about as 
basic as it can get, but it works! 

• I machined the throttle mechanism out of aluminum. The small lever that pulls the drill's 
trigger pivots around a 3" threaded ball plunger pin, where it passes through a hole in the 
middle of a 6" vertical plate (Figure J). The plate, in turn, extends down from the platform 
that holds the back of the drill. 

• At the bottom of the plate, a smaller plate has a guide hole that carries the throttle cable to 
the opposite end of the trigger lever. I filed the lever end round so its edges wouldn't mar 
the plastic trigger. 

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The Drill Rod 

Step 6 — Mount the drill. 

• The bike's rear wheel has a spring shock absorber, so I needed to mount the drill in a way 
that would allow it to move up and down along with the bike's swing arm. (The alternative 
would be to tighten the rear shock spring all the way down, disabling it — but this would 
make the ride extremely uncomfortable.) 

• To accomplish this, I designed a hinged platform that connects to the bike's seat post. 
Designing and making this flexible connection was the hardest part of the project. 

• The platform has 2 parts: a front bracket that clamps to the seat post, and the main 
platform that holds the drill. The bracket has a flat slot in back, and the platform has an 
axle that passes through the slot. 

• The rod is contained by the slot but is free to move inside, creating a combination slip joint 
and hinge. This supports the platform while giving it 2 degrees of freedom: up-down tilt 
(pitch) and forward-back translation (surge). 

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The Drill Rod 

Step 7 

• I machined the front bracket out of aluminum stock using my Smithy and made the axle 
out of some 3/8" rod, turning the ends with a threaded die and screwing matching knobs 
onto each end. 

• I pieced together the platform out of some scrap teak wood from a paper towel holder that I 
dumpster-dove at a marina. See design sketches for the hinge and platform in the zip file 
you downloaded earlier. 

• The rear part of the platform has a metal tongue for the bottom of the drill to hook onto, and 
2 pegs that cradle the drill on either side. The pegs are small lengths of dowel that I 
beveled with a file and glued into holes. 

• A separate curved piece of teak fits on top of the platform and swings around to cradle the 
back end of the drill, where it protrudes through the hole in the platform. 

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The Drill Rod 

Step 8 

• A support pillar connects the main platform down to the motor mounting plate. It's a 16" 
length of threaded rod tucked inside a slightly shorter length of square aluminum U- 
channel. At the top, the U-channel butts up against the underside of the platform. 

• The rod sticks up through holes in the platform and swing piece, and then threads through 
the washer, nut, and wing nut that tighten it down. 

• I attached the bottom of the support pillar to the gearbox mounting plate using 2 U-shaped 
clamps that I cut out of steel. 

• The clamps fit around the plate and U-channel, with a socket head cap screw to tighten 
them down together. The bottom end of the threaded rod rests on the topside of the bike's 
swing arm. 

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The Drill Rod 

Step 9 — Ride the drill rod. 

• One last modification: the seat that 
comes on the E-Punk is very 
small, so I installed a larger, 
spring-loaded seat. The Drill Rod 
was complete, ready to rev up and 

• The Drill Rod's speed is 
determined by the speed of its drill, 
the size of its rear wheel, and its 
gear ratio. I made a spreadsheet 
that let me see the results, in miles 
per hour, of changing each of these 
variables. My calculations: 

• Gear ratio = wheel sprocket 
teeth / gearbox sprocket teeth = 

• Wheel rpm = drill rpm / gear 
ratio = 1,800rpm/ (66/18) = 

• Wheel circumference = wheel 
diameter * n = 9" * n = 30.73" 

• Speed = wheel rpm * wheel 
circumference = 14,245" per 
minute / (63,360'Vmile) * (60 
minutes/hour) = 13.49mph 

• This speed is the absolute best 
case with no weight. With an adult 
rider, the bike's speed is closer to 
10mph. You can use a bigger 
gearbox sprocket to make it faster, 
but 10mph is plenty fast for me on 
something this small. 

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The Drill Rod 

Step 10 

i i 

• Note that keeping the E-Punk's 
original 7" back wheel would have 
made the bike's top speed only 
10.49mph (although the increased 
torque would mean less speed 
reduction from weight). 

• Note also that the original Electric 
Punk bike was made for kids, and 
is officially rated at 120lbs 
maximum weight for the rider. 

• I weigh 230lbs, and the Drill Rod 
handles my weight just fine. My 
son, who weighs more than I, also 
rides it successfully (his weight is 
being withheld for my safety and 

So how does it handle? I have cruised with the Drill Rod several miles so far, and it works just 
fine. Several friends have also tried it, and it always puts a big smile on their faces. I like to think 
this is because they're having fun, but perhaps embarrassment is involved. My son and son-in- 
law also both love riding the Drill Rod. Like me, they have no shame. 

One day I was cutting tree limbs hanging over a fence on my property, and a limb fell onto the 
neighbor's side of the fence. The way our homes are configured, I had to go halfway around the 
block to get to where I could pick up the limb, and I decided to ride the Drill Rod. On the way 
back home, I passed a city maintenance truck. The guy inside just stared and shook his head as 
if to say, "You know that people can see you, don't you?" 

The Drill Rod weighs 37lbs, including the weight of an extra battery, which fits easily in the frame 
where the original battery pack went. The little bike takes me 2 miles per fully charged battery. If 
you carry extra batteries, you increase your range 2 miles per battery. I did the math. 

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The Drill Rod 

Admittedly, the brakes that come on the E-Punk are terrible, and are inadequate for the Drill 
Rod. But between using the brakes and dragging your feet, you can get stopped. That being said, 
if you build one and run it into a tree, consider yourself forewarned. 

Meanwhile, I'm thinking about building a drill-powered dinghy. 

This project first appeared in MAKE Volume 21 . 

This document was last generated on 201 2-1 0-30 07:48:39 PM. 

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